The present invention relates to multi-address calling for transmitting the same information from an originating terminal to a plurality of destination terminals, and more particularly to a signalling system for a control signal related to the plurality of destination terminals, which is transmitted and received between the originating terminal and an exchange in such multi-address calling and a signal control equipment therefor which generates and receives the control signal and performs call control.
There have heretofore been proposed for multi-address calling (1) a sequential multi-address delivering system in which each destination terminal address and communication data are once stored in a terminal control equipment of an originating terminal, and paths are then connected to the destination terminals one after another to transmit thereto the communication data; (2) a stored data multi-address delivering system in which destination terminal addresses and communication data are stored in an exchange from an originating terminal and then the exchange connects the destination terminals one after another and transfers thereto the communication data upon each connection; and (3) a real time multi-address calling system in which an originating terminal is simultaneously connected to all of destination terminals to transmit communication data from the former to the latter at the same time.
For achieving these multi-address communication systems, use has been made of such signalling systems and control systems as follows: In an ordinary dialing system, each destination terminal address is dialed as by a ten-key keyboard for transmission; accordingly, in this system, it is necessary to successively dial many ordinary dial signals consisting of a plurality of figures, resulting in the operation becoming very troublesome. Further, this system requires processing for receiving and translating a plurality of dials in the exchange and the dial signal becomes long, and hence the transfer time therefor becomes long. In the case of (1) the sequential multi-address delivering system, it is necessary to employ a storage for storing the destination terminal address in the terminal control equipment. There has been proposed a push-button operating system in which a plurality of push buttons on a control panel have one-to-one correspondence to a plurality of destination terminals and are selectively depressed to generate the address of the destination terminal corresponding to the depressed push-button. In this case, it is necessary that information for the correspondence between the push-buttons and the destination terminals be held in the terminal control equipment and the address transmission control is complex and calls for expensive equipment; furthermore, it is necessary to receive and translate a plurality of addresses in the exchange and the transfer time is long. In a general or group multi-address calling system, destination terminals of general or group multi-address calling are connected to an exchange in advance and a signal of general or group multi-address calling is transmitted from an originating terminal. In this system, the signal is transmitted to all terminals or all terminals of the group and it is impossible to select at will the destination terminals call by call. Moreover, any of the above systems do not have a function of transmitting to the originating terminal information about a call from each destination terminal.
Japanese Patent Kokai (Laid-Open) Gazette No. 65711/74 (June 26, 1974) discloses the following signalling system. From an originating terminal are sent out N bits, which have one-to-one correspondence to destination terminals, and those of the N bits corresponding to the destination terminals desired to call are set, for example, to "1" and the bits corresponding to the other destination terminals are set to "0". When receiving a selection signal of the N bits, an exchange switches its contacts for the destination terminals corresponding to the bits "1", thereby to call the destination terminals. The exchange informs the originating terminal of the call accepting state of each called destination terminals by a call accepting state signal of N bits which are each set, for example, to "1" or "0" depending upon whether the corresponding called destination terminal is call-accept or non-call-accept and which are arranged in the same order of the destination terminals as the abovesaid N-bit selection signal. The originating terminal detects the status "1" or "0" of each bit of the N-bit call accepting state signal to learn whether or not the called terminals have accepted the call. Such a signalling system markedly simplifies the operation in the originating terminal, reduces the operating time, does not require storing the destination terminal addresses in an originating terminal control equipment and permits real time multi-address calling to selected ones of the destination terminals. Further, this system is very convenient since the exchange transmits to the originating terminal the call accepting state signal in the form of an N-bit signal similar to the N-bit call request signal.
But the primary object of prior this system resides in that after receiving the call accepting state signal, the originating terminal sends out communication data only to the call-accept destination terminals and then automatically calls again the non-call-accept destination terminals at the calling party's request. To perform this, the system employs means for storing and indicating the called terminals, means for storing and indicating the call accepting state of each destination terminal based on the call accepting state signal, means for retaining the memory of the non-call-accept ones of the terminals appointed to call and removing the memory of the other terminals by the sending out of the communication data, and means for calling again the non-call-accept destination terminals based on their memory retained in the abovesaid means. But the gazette makes no mention of how the N-bit selection signal and the N-bit call accepting state signal are produced and delivered. Furthermore, in the exchange is provided a special switch for selecting either a switching network or a trunk for multi-address calling; in the multi-address calling, the switch is changed over to the side of the trunk, by which the communication data transfer is performed without passing through the switching network, that is, use is made of a connection different from an ordinary one. Accordingly, it is difficult for all terminals accommodated in the exchange to be used as destination terminals of the multi-address calling.
Moreover, this prior signalling system possesses the afore-mentioned features but information from the exchange to the originating terminal is limited specifically to the call accepting state signal. For example, in the case of sending facsimile data by one-to-one communication, the originating terminal makes a telephone call to the destination terminal to confirm that the facsimile data is surely received by the destination terminal. Such confirmation is important but has not been practised in the past since it is very troublesome because of a large number of destination terminals in the multi-address calling.
It is an object of the present invention to provide a signalling system for multi-address calling by which various signals related to a plurality of destination terminals, which are transmitted and received between an originating terminal and an exchange, can be delivered with small amounts of data, in a standardized, simple format and in a short time.
Another object of the present invention is to provide a signalling system for multi-address calling by which a plurality of destination terminals can be called easily and in a short time and not only the call accepting state but also the data receiving state of each destination terminal can be transmitted by control signals of a standardized format from an exchange to an originating terminal.
Another object of the present invention is to provide a signal control equipment for multi-address calling with which a control signal related to a plurality of destination terminals, transmitted from an exchange, are detected and indicated in an originating terminal for each destination terminal.
Another object of the present invention is to provide a signal control equipment for multi-address calling in which the burden on a central processing unit on the side of an exchange is relatively light and the processing time for a control signal is short.
Still another object of the present invention is to provide a signal control equipment for multi-address calling with which an originating terminal can be connected by an exchange to a destination terminal in the same manner as an ordinary connection, and accordingly desired ones of destination terminals registered in the exchange in advance can be used as destination terminals of the multi-address calling.